Migrate OnSubscriptionsChangedListener to different Handler

Remove calls to the internal method of OnSubscriptionsChangedListener.
This causes a minor change to the threading since posts now go through
the same handler twice, but it should be benign and thread safer.

Bug: 278814050
Test: atest FrameworksTelephonyTests
Change-Id: I3081003ec6092334df9dca7833ed53b96d313b98
diff --git a/src/com/android/phone/ImsStateCallbackController.java b/src/com/android/phone/ImsStateCallbackController.java
index edad754..019c1ca 100644
--- a/src/com/android/phone/ImsStateCallbackController.java
+++ b/src/com/android/phone/ImsStateCallbackController.java
@@ -739,7 +739,7 @@
         updateFeatureControllerSize(numSlots);
 
         mTelephonyRegistryManager.addOnSubscriptionsChangedListener(
-                mSubChangedListener, mSubChangedListener.getHandlerExecutor());
+                mSubChangedListener, mHandler::post);
 
         PhoneConfigurationManager.registerForMultiSimConfigChange(mHandler,
                 EVENT_MSIM_CONFIGURATION_CHANGE, null);